1. Field of the Invention
The invention relates to pneumatic impact forming tools, and more particularly to the monitoring of actuating pressure therein for purposes of generating signals representative of the operating performance thereof.
2. Description of the Prior Art
In a typical pneumatic impact forming tool, pressurized gaseous fluid is delivered to a working cylinder upstream of a ram piston contained therein. The pressurized gaseous fluid generates kinetic energy by accelerating the ram piston forwardly in the working cylinder. The kinetic energy is transferred to impact energy upon contact of the ram piston with a workpiece resulting in a plastic deformation thereof. Thereafter, the ram piston is rearwardly moved in the working cylinder to restore the operating energy of the gaseous fluid and the work cycle is sequentially repeated.
A pneumatically controlled riveting gun, for example, utilizes a chisel which is coupled to the working cylinder. The ram piston located therein is accelerated by the pressurized gaseous fluid to impact the chisel which in turn plastically deforms part of a rivet impacted thereby during each work cycle until the rivet is ultimately processed to the desired form. Similarly, other pneumatically controlled tools such as forging hammers operate with the same work cycle; except in these tools, the dies used to form the workpiece are permanently attached to the ram pistons and the kinetic energy thereof is delivered directly to the workpiece.
A typical example of a pneumatic riveting gun process is in the manufacture of steam turbines wherein blades are fitted in relation to one another around their outer edge by a shroud. The shroud is fitted over the blade tenons which are then deformed by a pneumatically controlled riveting gun to form rivets holding the shroud in place. It is of particular difficulty to determine consistency in the production of each unit especially considering the varying air supply pressure due to the many other pneumatic tools operating therefrom and the dirt particles which are at times introduced into the work cylinder by means attached thereto. Presently, this difficulty is overcome by quality control methods but, in general, these methods are time consuming and costly. Another method of relieving this problem of quality inconsistency is to monitor the performance of the pneumatic tool during each operation. More specifically, it would be desirable to generate signals representative of the performance of the pneumatic tool during one or more working cycles as a function of the actuating pressure monitored therefor.
The impact energy produced by the pneumatic tool must first overcome the elastic deformation of the workpiece before said energy can plastically deform or permanently shape the workpiece. In the foregoing riveting gun example, it is important that the amount of energy delivered in each work cycle be lare enugh to cause sufficient plastic deformation of the tenon to allow completion of riveting process in as few strokes as possible. Not only will this save time and expedite the process, but it also limits the effects of any elastic wave propagation resulting from the work strokes of the pneumatic tool impacting the workpiece. These elastic waves propagating through material may cause at times weakening effects to said workpiece. Therefore, a system to generate signals representative of the energy delivered to the workpiece per one or more work cycles would be desirable. With said representative energy values, a correlation of delivered energy with rivet quality could be made available thereby providing data for calibrating a pneumatic tool to ensure deliverance of a quality amount of energy to a workpiece during day-to-day operations.
It is understood that the impact energy of a pneumatic tool must be adjusted to control the impact forming process on workpieces of varying sizes and shapes. For example, when dealing with smaller more easily formed material, the impact energy required may be less and should the pneumatic tool be incorrectly calibrated, a rapid work cycle repetition rate may result effecting an uncontrollable impact alignment on the workpiece. Here again, supplied with the energy delivered to the workpiece over one or more strokes, one may correlate said energy with both the controllability of the pneumatic tool and the quality of the workpiece formation according to size and shape. Quality reproducibility may be increased over the broad spectrum of workpieces.
Normally, pneumatic tools include automatic lubrication systems wherein the lubrication oil is permitted to flow into the work cylinder as needed by some valving arrangement. Unfortunately in some cases, the lubricating oil may erode its rubber tubing supply lines thus causing dirt particles to be introduced to the work cylinder. Other unwanted particles may be supplied at times through the air supply lines connected thereto. Foreign particles in the working cylinder will promote inefficient operation of the tool and possibly cause the tool to be shut down for repairs. It is recognized that pneumatic tools are generally very rugged, however, there have been cases when dirt particles have accumulated sufficiently in the lubricating oil supply line to clog the lubricating oil input valves whereby little to no lubrication was provided to the working cylinder. When these conditions persisted undetected for lengthy periods of time, it was observed that the barrel of the working cylinder was severely scored, at times beyond repair. It is apparent that primary emphasis should be directed to providing a system which could provide some representation of increasing frictional forces. Such a system could indicate an operational problem prior to any harmful effects caused thereby. This type of monitoring system could lead to an increase in availability and production output of said pneumatic tool.